Since silicone rubber is excellent in heat resistance, flame resistance, chemical stability, weather resistance, radiation resistance, electrical properties, and the like, it has been used for a variety of uses in a wide range of areas. In particular, since silicone rubber is physiologically inactive and reacts little with body tissues when the silicone rubber is in touch with a living body, it has been used as a material for medical instruments such as medical catheters.
The medical catheter is a tube which is inserted into a body cavity such as a thoracic cavity and an abdominal cavity, a lumen such as an alimentary canal and a ureter, and a blood vessel, and used to discharge a body fluid, or injecting or dripping a drug solution, nutrition, or a contrast medium. The medical catheter is required to have scratch resistance (tear resistance), kink resistance (tensile strength), transparency, flexibility (tensile elongation properties), and the like, in addition to biocompatibility. Specifically, the medical catheter is used as a drainage tube of an aspirator for removing an effluent such as blood, and pus after a surgery operation, and a tube for intaking nutrient after a surgical operation such as percutaneous endoscopic gastrostomy (PEG). In addition, in order to make silicone rubber for an extremely fine tube as a catheter, the silicone rubber composition, which is a raw material of the silicone rubber, is required to have extrusion molding properties.
As a material for medical catheters, soft polyvinyl chloride is also widely used in addition to silicone rubber. Compared with polyvinyl chloride, silicone rubber is excellent in biocompatibility and flexibility, but required to have improved strength such as tear resistance, and tensile strength, in particular, tear resistance. When the tear resistance is insufficient, the catheter may be torn by the damage made by a needle or a blade used during a surgical operation. When the tensile strength is insufficient, the catheter may be bent and closed (kinked), and thereby, a flow of a body fluid which should be discharged or a drug solution which should be injected may be stagnated.
Therefore, in order to improve the tear strength and tensile strength of silicone rubber, various methods have been suggested (for example, Patent Documents Nos. 1 to 8).
For example, Patent Document No. 1 discloses a hardening silicone rubber composition which contains mainly organopolysiloxane having high viscosity and containing a small amount of a vinyl group (crude rubber (A)), and is added with organopolysiloxane having low viscosity and containing a large amount of a vinyl group (silicone oil (B)), an organopolysiloxane copolymer containing a vinyl group (silicone resin containing a vinyl group (C)), organo-hydrogen siloxane (crosslinking agent (D)), platinum or a platinum compound (hardening catalyst (E)), and fine powdered silica (filler (F)).